1. Field of the Invention
The present invention relates to a system for obtaining autologous plasma from a patient during surgery. The invention further relates to a method for preparing fibrin gel and other hemostat or tissue sealant preparations from the autologous plasma.
2. Background Information
Preparations of human coagulation factors including fibrinogen and thrombin, have been used extensively in surgery over the last ten years. These biological fibrin sealants (also known as fibrin glue, fibrin adhesive, or fibrin tissue sealant) promote hemostasis and wound healing by sealing leakage from tissues, sutures, staples, and prostheses and are particularly useful during open heart surgery in heparinized patients. The sealants also have limited use as an adhesive for the bonding of tissues and they reduce the amount of blood required for transfusions by controlling intraoperative bleeding. Their effectiveness is reflected in the extensive range of surgical applications for which they have been used, including cardiovascular surgery, plastic surgery, orthopedics, urology, obstetrics and gynecology, dentistry, maxillofacial and ophthalmic surgery.
Fibrin sealant products can be prepared from pooled human plasma. However, such preparations potentially risk transmission of HIV, hepatitis B and other serologically transmitted illnesses. Also, in some instances these preparations could cause immunologic reactions.
As an alternative, some hospitals are preparing fibrin sealant in-house using the patient's own blood (autologous) or single-donor (homologous) plasma as a source of fibrinogen and Factor XIII. The components are typically prepared by freezing plasma at temperatures below -20.degree. C. overnight, slowly thawing the material at 0-4.degree. C., centrifuging, and transferring the cryoprecipitate to a syringe or spray container. The procedure usually requires several hours, making the product unavailable for emergency cases. The lengthy manipulations currently required to generate fibrin sealant also introduce the risk of contaminating the product and transmitting viral infections to the technicians involved.
The thrombin, usually purified from bovine plasma, can be obtained commercially and is typically prepared in a separate syringe or spray container. The two solutions are delivered simultaneously or alternately to generate fibrin sealant at the site of the wound.
The hemostatic efficacy of fibrin glue has been well established. Autologous fibrin gel, made from plasma rather than a fibrinogen-containing precipitate, appears to have comparable hemostatic properties to traditional fibrin glue as well as valuable sealant properties. For instance, fibrin gel is useful in sealing air leaks in pulmonary procedures.
In preparing fibrin gel, plasma is typically obtained from autologous blood following centrifugation for about ten minutes to separate blood cells from anticoagulated blood, followed by removal of the plasma. Centrifugation in the operating room, however, may be inconvenient because of the required instrumentation, potential for aerosolization with its concomitant contamination risks, and difficulty in decontaminating instrumentation between procedures. If centrifugation takes place external to the OR, aseptic transport of the plasma fraction to the operative site is required.
Hollow fiber devices permitting separation of plasma from blood without the need for centrifugation have been used for plasma exchange therapy (PET). In PET, the separated plasma is eliminated and the separated blood cells with replacement fluids are returned to the patient.
Recently, hollow fiber filtration technology has been developed to meet the requirements of cell separation from cell cultures--including shear-sensitive mammalian cells--while allowing free passage of soluble proteins. This membrane technology offers an alternative to centrifugation, precipitation and conventional filtration techniques for bioseparations, eg. The processing of fermentation products, and is available for small volume applications. Sterilizable, disposable filtration modules are available from at least one manufacturer.